Brake control device



Dec. 26, 1939. J. w. STAUFFER 2,184,563

BRAKE CONTROL DEVICE Filed Dec. `15, 195'/ Il 'Ir/11114 1,1',

nl YI Patented Dec. 26, 1939 nuire srr'es 2,184,568 n BRAKE ooN'rao'LDEVICE JayWarren Staunen', EaStMcKeeSport, Pa., assignor to TheWestinghouseAir Brake Company, Wilmerding, Paga corporation of Perm-Sylvania Application December l5, 1937, Serial No. 179,929

27 Claims.

shoes are applied to the wheel treads with a giveny force, the resultantdegree of braking eiect is relatively lower when the Vehicle or train istraveling at a high speed than when the vehicle or train is traveling ata low speed. This is due `to the fact that the coefficient of frictionbetween vthe brake shoes and vehicle wheel treads is lower at highspeeds than at low speeds. Because of this phenomenon, if the brakes areapplied to Aa high degree at a high speed, the braking force must bereduced as the speed of the train or vehicle diminishes, orotherwisesliding ofthe wheels may result. Wheel sliding is objectionablenot onlyl because of the damage resulting to the wheels,

but also because the retarding effect produced by Ia sliding wheel isless than that produced by a rolling wheel, which necessarilyincreases'the length of the stop.

In order to minimize the danger yof wheel sliding, and to at the sametime produce a comparatively short and uniform stop, there hasheretofore been proposed a brake equipment in which the degree of thebraking effect has been reduced in predetermined steps as thespeed ofthe train or vehicle diminishes. A brake equipment of this type isillustrated and described yin the pending application or" Ellis E.Hewitt, Serial No. 88,698, led June 30,1935, and assigned to theassignee of the present application. I

Brake systems embodying the features disclosed in the Hewitt applicationhave been' in use forl several years and have under the most severeservice conditions demonstrated their utility beyond question. However,in the design of such brake systems it is apparent that certainassumptions must be made with respect to the tractive condition of therails to be encountered, with the result that if the rail conditionsencountered are universally better than that assumed full advantagecannot be taken of these conditions to produce shortest possible stop,while on the other hand if rail conditions are below that assumed theforce with which the brakes are applied may,

be toc high for the existing track conditions and some wheel sliding mayresult.l v v v In carrying forward my invention I propose to providemeans for detecting at all times during ad brake applicationwthetractive condition of the rails and to thereupon instantly,` andcontinuously,

establish the permissible limit to which the brakes may be applied, thusenabling the -brakes to'beff' appliedmore precisely according totheactual condition of the rails existing throughout the stop.

It is accordinglya prime object of the present invention to provide abrakesystemin which the permissible maximum degree of application of thebrakes is established ymore nearly according to the actual tractivecondition of the rails over which `the train orvehicle ispassing at theltime the brakes are applied. y'

jAjfurther object of the `invention isto provide;

va novel means for detect-ing the tractive condition of theurails overwhich the vehicle or/ train is passing at the time the brakes areapplied-and to associate said mean'sx lwith the control of the brakes soas toI at all times during the application;

prevent the degreeY of 'the application from exceelding a value which islikely to produce sliding of the wheels. f

A yet further object of the invention is to provide means for detectingthe tractive conditionof the railsifor each instant during the brakeapplication, and for reducingthe 'degree of the application asthetractive condition becomes bad and for increasing` (within limits)thev degree of the application as the `tractive condition improves.

A still further object of vthe invention is to provide a brake systemwherein the degree of the brake application lis controlled both withrespect to the speed of the vehicle.(or train) and with respect to thetractive condition of the rails over.`

whichthe -vehicle or trainfis passing at and dur-n ling the time thebrakes are applied. 1

A `yet further object of the invention is 'to pro- Vide means'fordetecting the tractive condition'of the rails and for associating saidlmeanswith'a brake equipment of the type illustrated in theaforementioned Hewitt application, in a manner lsuch that the degree ofapplication of the brakes is' jointly controlled according to the speedof the vehicle (or train) and the tractive condition of the rail. v

Other objects of the invention, dealing'particularly withvthearrangement rand construction of parts, will be more fully understoodfromthe folf 'lowing description, which is taken in` connection with theattached drawing, wherein,

` Fig. 1 shows in schematic and diagrammatic form an embodiment of theinvention in a brake equipment illustrated for one car of a train.

Fig; 2 .shows a view of the rail-.engagingdevice ldiaphragm portion 2l,and a magnet valve por- Ytion28.

illustrated in Fig. 1, taken substantially along the line 2 2.

Referring now to the drawing, the brake system there illustratedcomprises' a brake cylinder l0, a control valve device Il, a tractiondetector device indicated in its entirety at I2, a speed controlledswitch device i3, two pressure operated valve devices I4 and l5, amagnet valve device i6, a pressure operated switch device l1, and a feedvalve device i8. Also shown are a supply reservoir i9, a tractiondetector reservoir 20, and

three volume reservoirs 2| 22 and 23, designated as volume reservoir No.1, volume reservoir No. 2, and volume reservoir No. 3, respectively. Thethree volume reservoirs differ in volume, as illustrated, for a purposeto be explained later.

Considering now more in` detail the parts above enumerated, the brakecylinder l0 is preferably of conventional design, and is arranged tooperate any type of friction brake (not shown) and while only one brake.cylinder has been illustrated it will be apparent that as many may beemployed as are found desirable. l

` Consideringnow the control valve device il, this device comprises arelay valve portion 26, a

Considering rst the relay valve portion, this portion includes a supplyvalve 23 and a release valve 30 for controlling the supply of fluidunder pressure to and its release from the brake cylinder il). Thesupply valve 29 is urged toward a seated position by a spring 3l and isprovided with a fiuted stem 32.engaging one end of a slidable plunger33. The other end of the slidable plunger engages' thev lower end of aleverl 34. In the position illustrated, the lower end of the lever 34rests between the right hand end of the plunger 33 and an adjustablestop 35.

The lever 34 is pivoted intermediate its end on a pin 36 which iscarried by a hollow cylindrical member 3?. The member 3l is slidable ina bore in the casing, and reacting between the 'casing and the member'3'1 is a spring 38. This spring acts to bias the member 3l to theright.

The upper end of the lever 34 is bifurcated to embrace a reduced portion39 of a stem 4U attached to or forming a part of the release valve 3i).The right hand end of the stem 40 is, as illustrated, recessedv toreceive and contain a biasing spring 4 l. This spring urges the releasevalve 38 and its stem 4E! toward the left, but the release valve is heldin an unseated position, for the condition of the parts illustrated, byaction of the spring 38.

The casing enclosing the parts just described defines a chamber 42 whichis in open communication with thevbrake cylinder l0 by way of pipe andpassage 43. With the release valve 3D unseated and the supply valve 29seated,; as illustrated, the brake cylinder lil and chamber 42 are incommunication with the atmosphere by way -of port 44. When the releasevalve 3B is seated and the supply valve 29 is unseated, communicationisestablished between the chamber 42 and the supply reservoir i9 by way ofpipe 45.

Considering next the diaphragm section 2l,

. this section comprises spaced, unconnected diaphragms 48, 49, 5l! and5l, having areas diminoperates with the member 54 to hold the twodiaphragme 48 and 49 in spaced relationship so as to denne a chamber 53.

The diaphragms 53 and 5l are, respectively, similarly provided withspacing members 5l and 58, which serve to hold these diaphragms inspaced relationship whereby there is dened between diaphragms 49 and 5i!a chamber 63 and between diaphragms 50 and 5l a chamber 6|. A capsecured tev the diaphragm section forms with the diaphragm 5l anotherchamber 33.

Now when uid under pressure is simultaneously supplied to the fourdiaphragm chambers 56, S3, 3l and 63 to the same degree, it will beapparent that the pressures on either side of each of diaphragme 49, E@and 5i will be balanced, and due to the fact that the diaphragme areunconnected and are therefore free to move individually, only thediaphragm 48 will be exed and it will accordingly move to the left.

In moving to the left the diaphragm 48 shifts the slidable member 3lwith it, whereupon the release valve 3i) will be iirst seated andthereafter the supply valve 29 will be unseated, to supply fluid underpressure to chamber 42 and brake cylinder l0. When pressure in chamber42 is substantially equal to the pressure in chamber 5%, the diaphragm4B will move to the right and permit supply valve 29 to be seatedwithout unseat-ing release valve 3i). Brake cylinder pressure willY thencorrespond to the pressure in chamber 5S.

If now the pressure in the chamber 5E is reduced to zero, while theoriginal pressure is maintained in, the other chambers, the pressures oneither side of diaphragm 49 will no longer be balanced, and due to thefact that this diaphragm is smaller in area than the diaphragm 48, theoverbalancing pressure acting to the left of diaphragmll will shift itto the right and thus unseat the release valve 3|). Fluid under pressurewill be released from the brake cylinder l0 and chamber 42 until suchtime as the pressure acting to the left of diaphragm 48 is balanced bythe 45 pressure actingto the right of diaphragm 49. When this conditionobtains the release valve 30 will be seated whereupon brake cylinderpressure will bear to the pressure in chamber El) the same relation thatthe area of diaphragm 43 bears to,A

be apparent that brake cylinder pressure will be,

reduced until it bears to the pressure in chamber 6l the same relationthat the area of diaphragm 50 bears to the area of diaphragm 48.

In a like manner, if the pressure in chamber 5l is subsequently reducedto atmospheric pres-l sure, while the original pressure is maintained inchamber 63, brake cylinder pressure will be reduced until it bears tothe pressure in chamber 63 the same relation that the area of diaphragmr5l bears to the area of diaphragm 48.

It will thus be apparent that upon initially supplying fluid underpressure to a like degree to each of the chambers 56, 63, SI and 63 theinitial brake cylinder pressure established will be equal to theunitpressure in any one of these chambers, and that upon subsequently andprogressively reducing the pressure in each of these chambers toatmospheric pressure, in the order named, brake cylinder pressure willbe reduced progressively in predetermined steps, established vac-.falaises unit designated by the numeral 69,while lthe low speedelectromagnet' 6l Aoperates a valve unit 4designatedby the numeral lil.

When Ythe high speed electromagnett is deenergized, a spring 1I holdsthe valve ,unit |53 in its upperlposition, `as illustrated, in whichcase diaphragm chamber 56 ilsiplaced in communication with theatmosphereby way ofpassage 73 and restricted portie. When the highspeedelectromagnet 65 is energized, the valve unit GS is shifted to its lowerposition, in which case the communication between thechamber 'and theatmosphere is closed, and'thechamber 5t is placed in communication withpipe and passage 12.

When the middle speed electromagnet 65 is deenergized, spring I5 holdsthe valve unit 65 in the upper position illustrated, in which casediaphragm chamber B9 is placed in communication with the atmosphere byway of passage '56 and restricted port TI. When the middle speedelectromagnet 166 is energized, this communication to the atmosphere isclosed and the chamber 69 is placed in communication with the pipe andpassage 12.

When the low speed electromagnet G1 is deenergized, spring 'I8 holds thevalve. unit lll in the upper position illustrated, in which casediaphragm chamber 6I is placed in communication with pipe and passage12. When the electromagnet El is energized, the valve-unit'll is shiftedto its lower position in which case communication between pipe andpassage I2 and chamber 6I is closed and chamber EI is con nected to theatmosphere by way of passage "l5 and restricted exhaust kport 89.

It will be observed that in the upper portion of the diaphragm sectionZIthere is provided three spring seated check valves 8|, 32 and-83.

These check valves provide, respectively,fa o-neway communication fromeach of diaphragm chambers 55, 6|) and 6I to pipe and passage l2, sothat fluid under pressure may be released from these chamberssimultaneously with the release of uid under pressure from pipe andpassage i2 at a time when the valve unitsil, 69 and 'I9 have closedcommunication between the pipe and passage l2 and the chambers.

Considering now the traction detector device I2, this device ispreferably mounted upon an unsprung frame member of the vehicle truck.

Secured to this unsprung truck frame member is a cylinder 81, and withinthe cylinder is a piston S3 subject on its uppermost side `to pres sureof fluid in a chamber 89 and on its lowermost side to pressure oi alight biasing spring SQ disposed in a chamber normally at atmos- To thepiston 88 is secured a stem 9|, the lower :pressure in aY chamber H6normally open to the 94 so that `the. shoe`951may'1movelongitudinallywith respect to the piston stem 9|.

Also mounted on the-:truck frame .member 86 4 'isa contactv arm member|99, which is-pivotally f; mounted .intermediate its ends at I0 I toabracket .|02 secured tothe truck frame member.

rIhe lower vendA of the arm is connected :loyna rod Iil3yto the shoe.95, and ,also` to one-endiota lcalibratedspring 191i. The opposite .endofthe spring Hifi is connected to VAan adjusting screw y 51195: carriedby an armk |95 formingfa'part o-fthe bracket |92.

Insulated from and carried bythe upper .end of thezarm It@ are threecontact segmentsr |01,

|198 and lili?. 'Ihese contact segments are adapt-V` edto engage,respectively, with three `sets of stationary'contacts Hi), III and' H2,inthe inverse-cf the order named.

When fluid under pressure is supplied to the uw chamber 39 oftliecylinder 97, the shoe 95is depressed into engagement withv thetrack; rail 99. The force with which the shoe 95 engages the raildepends upon the pressure in the-chamber 89. Asvthe vehicle movesalongthe rail the n resultant force of friction between the shoe 95'):and rail 96 causes theshoe 95 to movelongitudinally with respect to `thevehicle againstzthe opposition of the calibrated spring |6115. `Themovement of the shoe thus rotates the arm Ilm. I

If it is assumed that the vehicleis travelingim rintheydirectionindicated by the arrow marked Direction of travel, then theforce of friction acting upon the shoe-95V will be in the directionofthe vdotted arrow marked Force of friction.

yments engage one or more of the contact sets.

The :point of importance to note, however, is thatv the angular positionof thearm It!) wi1l-2-45 (for a given speed range) correspondsubstantially tothe force of friction acting upon the shoe 95 and thusaccording to the tractive condition ofthe rail, because it will beobvious that' for a given pressure in the chamber 89 the forcei550 offriction acting on the shoe $5 will (for a given speed range) dependsubstantially upon the'condition of the rail.

.Considering now the pressure operated valve ,4 device lli, this deviceis embodied in a casing'" having disposed therein a piston I I t subjectA on one side to pressure of fluid ina chamber H5, and on the oppositeside to the atmospheric atmosphere by way of port I ll. The piston H4 60isfprovided with a stem IIB engaging a valve H9, which valve is normallyheldin anupper position by a spring 29.

-cmnmunication is established between the feed valve device I8 and thetraction detector reservoir 29. Upon supplyfof fluid at a lowpressure',` as for example ten pounds, to the chamber I I5, the valve' II9 is actuated to lower seated positionarlo to close communicationbetween the .feed V-valve device and the'traction detector reservoir. Asthe valve H9 ymovesto lower seated position the .seal between, stem H8and the bore in 'which .it moves is close enough toprevent lossof.pres-:5,15

sure from the traction detector reservoir to the chamber I I6.

The pressure operated valve device I5 is similar to the valve device I4,being also provided with a piston |22 subject on its uppermost side topressure of fluid ina chamber |23 and on its lowermost side to theatmospheric pressure in a chamber |24 normally open to the atmosphere byway of port |25. The piston is provided with a stem |26 engagingr avalve unit |21, which valve unit is normally urged to an upper positionby a spring |28.

In the illustrated position of the valve unit |21, communication is'established between a pipe |29 and the atmosphere by way of port |25.Upon supply of a fluid at a low pressure, as for example ten pounds, tothe chamber |23, the piston |22 actuates valve unit |21 downwardly toclose communication between pipe |29 and the atmosphere, and to opencommunication between the traction detector reservoir 20 and the pipe|29.

The magnet valve device 6 comprises -three electromagnets |30, |3| and|32 hereinafter designated for convenience as the I-I, M and Lelectromagnets. The H electromagnet controls operation of a double beatvalve |33, the M electromagnet |3I controls operation of va double beatvalve |34, while the L electromagnet controls operation of a Valve unit|35.

When the H electromagnet |30 is deenergized a spring |36 holds thedouble beat valve |33 in upper seated position, in which case volumereservoir No. l is connected to the pipe |29. When the H electromagnetis energized this communication is closed and volume reservoir No. 1 isconnected to the atmosphere by way of exhaust port |31.

When the M electromagnet 3| is deenergized a spring |38 holds the doublebeat valve |34 in upper seated position in which case volume reservoirNo. 2 is connected to pipe |29. When the M electromagnet is energized,this communication is closed and volume reservoir No. 2 is connected tothe atmosphere by way of exhaust port |39.

When the L electromagnet |32 is deenergized, a spring |40 holds thevalve unit |35 in the upper position illustrated, in which case volumereservoir No. 3 is connected to the atmosphere byl way of exhaust port4|. Upon energization of the L electromagnet the valve unit is shiftedto lower position, closing communication to the atmosphere andconnecting Volume reservoir No. 3 to the pipe |29.

Considering now the speed controlled switch device I3, this devicecomprises a stem |45, preferably made of electrically insulatingmaterial such for example as Bakelite or hard rubber, and slidable in abore in a stationary frame part |46. Secured to the stem |45 is a collar|41 and acting between the frame part |46 and this collar 41 is a spring|48. Disposed below the collar |41 and supporting the lower end of thestem |45 is a rotatable member |49. This member carries pivotallymounted thereto two fly-ball weights I 50.

shift the stern |45 upwardly a distance dependent upon the compressionof spring |48. As the speed of the vehicle diminishes the force actingon the underside of the collar |41 also diminishes, and spring |48shifts the stem |45 downwardly. The vertical position of the stem |45depends upon the speed of the vehicle.

Rigidly secured to the uppermost end of the stem |45 is one member of aset of contacts |52. Loosely disposed on the stem |45 is a contact plate|53 which is adapted to engage stationary contacts |54 and is movable onthe stem |45 between two collars |55. A spring |56 biases the contactplate |53 in an upward direction.

Also loosely disposed on the stem |45 is a second contact plate |51.This contact plate is adapted to engage two stationary contacts |58 andis movable between the lowermost of the two collars |55 and anothercollar |59. A spring |50 biases the contact plate |51 in a downwarddirection.

The parts of the speed controlled switch device are so arranged thatwhen the Vehicle is traveling above a certain high speed, as for examplesixty miles per hour, the contacts |52 are closed, and the contact plate|53 engages the stationary contacts |54, while the contact plate |51 isout of engagement with the stationary contacts |58.

At the instant the vehicle speed diminishes below sixty miles per hour,contacts |52 are f opened but contact plate |53 remains in engagementWith stationary contacts |54, while contact plate |51 is still out ofengagement with contacts |58.

When the vehicle speed diminishes below an intermediate speed, as forexample forty-live miles per hour, contact plate |53 disengages fromcontacts |54, while the contact plate |51 has not yet engaged thestationary contacts |58.

When the vehicle speed diminishes to a low chosen speed, as for examplefifteen miles per hour, the contact plate |51 engages the stationarycontacts |53.

Considering now the pressure operated switch device i1, this device isembodied in a casing containing a piston |62 subject on its lowermostside to pressure of uid in chamber |63 and on its uppermost side topressure of a spring |64 disposed in a chamber normally open to theatmosphere.

The piston |62 is provided with a stem |65 which carries insulatedtherefrom one member of a set of contacts |66. As will be observed, thecontacts |65` control communication between a battery |61 and the speedcontrolled switch device I3. The contacts |66 are normally held open bythe spring |64, but upon supply of fluid at a low pressure to thechamber |63, as for example three or four pounds pressure, the p-iston|62 is actuated upwardly to close contacts |66. It will be observed thatthe switch device |1 is connected to the aforementioned pipe 12, whichfor convenience will be termed a brake application pipe.

Considering now the electric circuits illustrated, it will be observedthat the contacts |52 of the speed controlled switch device |3 and thecontacts |01 and ||0 of the traction detector device |2 jointly controla circuit leading to the high speed electromagnet 65, which circuitcomprises conductors |10 and 1|. The contacts |53 and |54 of the speedcontrolled switch device and the contacts |08 and ||I of the tractiondetector device jointly control a circuit leading to the middleelectromagnet 66, which circuit includes conductors |13 and |14. Thecontacts |51 and |58 of the speed controlled switch device and thecontacts |09 and ||2 of the traction detector device jointly control thecircuit leading to the low speed electromagnet 61, which circuitincludes conductors |15 and |16.

In addition to the control just mentioned, the contacts 52 of thespeedcontrolled switch device also control a circuit |11 leading to theH electromagnet |3, and contacts |53 and |54 control a circuit |13leading to the M electromagnet |3I, while the contacts |51 and E58control a circuit |19 leading to the L electromagnet |32.

In all cases, it will be observed that one terminal of the battery |61is grounded as is one terminal of each of the electromagnets referredto, so that circuits are completed when the contacts mentioned areclosed.

Operation When the train or vehicle is running` under power, or iscoasting, the brake application. pipe 12 is maintained connected to theatmosphere, in which case the several parts of the control valve deviceare conditioned as illustrated. The brake cylinder l0, or brakecylinders, will be connected to the atmosphere and as a result thebrakes will be released.

Supply reservoir I9 will be maintained charged in the usual manner, andthe feed Valve device |8 will deliver fluid to the traction detectorreservoir 2i? at pressure corresponding to its setting. The feed valvedevice |8 is employed so as to limit or vary the pressure to which thetraction detector reservoir may be charged, to suit the design of thetraction detector parts, and so that the pressure therein may beadjusted for diiferent pressure values in the supply reservoir.

Assuming that the vehicle is traveling at a relatively high speed, asfor example in` excess of the sixty miles per hour heretofore mentioned,the other parts of the equipment will be in the positions illustrated.

When now it is desired to effect van application ofthe brakes, fluidunder pressure is supplied to the brake application pipe 12 to a degreein accordance with the desired degree of the brake application. When alow pressure (e. g. three or four pounds) has been established in thebrake application pipe the switch device i1 will close its contacts,|66, and since it was assumed that the vehicle was traveling in excessof sixty miles per hour will be obvious that conductors |18 and |13 willbe connected to battery itl, but circuits to each of the high speedelectromagnet B5 Vand the middle speed electromagnet ES will not beimmediately established because of the open contacts in the tractiondetector device |2. These electromagnets will remain deenergized andtheir valve units and |35 will remain in the upper position. Fluid underpressure supplied to the brake application pipe can then iiow only tothe diaphragm chambers 5| and 63. As before described, the control valvedevice will then operate to supply fluid under pressure to the brakecylinder to a degree which bears to the pressure of uid in the brakeapplication pipe the same relation that the area oi diaphragm 50 bearsto the area of diaphragm 48.

Upon the establishment of a low pressure in the brake cylinder, as forexample ten pounds, the two pressure operated valve devices I4 andv |5will operate to shift their valve units |9 and |21, respectively, to thelower position. The valve device I4 functions to isolate the tractiondetector reservoir 2|) from, the feed valve device i8, while the Valvedevice-l5 functions to connect the traction detector reservoir to thepipe |29 and thus to the cylinder 81.

Withthe vehicle traveling in excess oi sixty miles per hour, both the Helectromagnet illand the -M eleetroniagn'et |3| will be energized, whilethe L-electromagnet |32 will be deenergized. As a'resu'lt,`neither ofthe volume reservoirs 2|, 22 andEV-will. be connectedto the pipe 52a.The traction detector reservoir 2G will therefore equalwith the cylinder81, and a maximum preosine'will be produced in chamber 39.k will.therefore be depressed into engagement with railli with a maximum force.

If ynow 'at thetiinethe brake application is initiated bad railconditions exist, the force of frictionwacting on the shoe will berelatively low.

The shoe 95 If the forceof frictionisso lowthat the arm |013` y is notrotated far enough for contact ||1to engage contacts I@ it will beobvious that the'high speed Yelectromiagnet i'will not be energized alethough thevehicle speed is in excess of sixty miles per hour. If therail conditions are very bad contact 68 may not engage contacts i i, inwhich case the middle speed electromagnet |56 will not be energized.Thus if the initial condition of the rails is bad the initial degree towhich the brakes may beapplied is limited. If the initial rail conditionis good, then arm lil@ will swing in a clockwisedirection far enough tocomplete the circuits tothe high and middle electromagnets, andas aresult the valve device will establish a brake cylinder corresponding tobrake application pipe pressure, as heretofore described.

Assuming now that good rail conditions exist initially and throughoutthe entire stop, it will` be obviousthat when the speed of the vehiclediminishes to slightly below sixty miles per hour, contacts- |52'willvbe opened and the high speed electromagnet 65 will be deenergized. Asya result, brake cylindery pressure will be reduced by the rst stepprovided for by the diaphragm arrangement incontrol valve device I Atthe same time, the opening of contacts |52 deenergizes the Helectromagnet |30, so that y.Volurne reservoir No. l is placedin'communication with pipe |29. The traction detector reservoir isnow-in communication with the cylinder 81 and the volume reservoir No.l, so that the equal-- ization pressure diminishes to a lower value thanexistedk before. This reduces the pressure with which ythe shoe S5 ispressed into engagement with the track rail.

The purpose'of reducing the pressure acting on theshoe 95 is tocompensate for the increasing coeicient of friction between the shoe andrail as the speed of the vehicle diminishes. If such a compensation werenot madethe arm lili! .would be gradually rotated progressively in aclockwise direction asy the speed of the vehicle diminishes and thevcoefficient of friction between the shoe and railincreases.- It wouldthen measure the increasing coefiicient of friction rather than thetractive condition of the rail.

As the speed of the vehicle diminishes to fortyfive miles per hour,.contact plate 53 disengages from stationary contacts |56, andaccordingly the middle speed electromagnet Ei and the M electromagnet-|3| are both deenergized. Deenergization of the middle speedelectromagnet 65 `effectsv a'further step reduction in brake cylinderpressure, while vdeenergization of the M electromagnet |3| effects areduction in the pressure in cylinder chamber 89by connecting volumereser- 75 voir No. 2 in parallel with the traction detector reservoir20, volume reservoir No. 1 and cylinder 81.

In a similar manner, when the vehicle speed diminishes to fteen milesper hour, contact plate |5'I engages stationary contacts |58, whereuponthe low speed electromagnet 61 and the L electromagnet |32 are bothenergized. A further reduction in brake cylinder pressure is establishedas well as a further reduction in the pressure of fluid in chamber 89.

Thus it will be observed that as the speed of the vehicle diminishes,with good rail conditions maintained throughout, brake cylinder pressureis reduced in a series of predetermined steps, and at the same time theforce acting to hold shoe in engagement with the rail is likewise andsimilarly reduced to compensate for the increasing coefficient offriction between shoe and rail.

If now at any time during the brake application bad rail conditions areencountered, the force of friction acting upon the shoe 95 will beaccordingly diminished. As a result, the arm |00 will be caused torotate in a counterclockwise direction to sequentially open one or moreof the circuits to the high speed, middle speed and low speedelectromagnets of the control valve device. In the event that any one ormore of these circuits have already been opened by operation of thespeed controlled switch device I 3, the opening of the traction detectorcontacts will have no eiect. But if the traction detector contacts areopened ahead of those of the speed controlled switch device, it will beapparent that the maxi- -mum permissible limit to which the brakes maybe applied will be reduced.

Thus the degree to which the brakes may be applied is limited not aloneby the action of the speed controlled switch device I3, but is alsolimited by the action of the traction detector device I2.

It is to be particularly noted that the traction detector devicefunctions to determine the tractive condition of the rails for everyinstant throughout the entire stop. If during a given speed range, asfor example between forty-five and sixty miles per hour, bad railconditions are rst encountered, and then the rail conditions immediatelyimprove, the traction detector device will first operate to reduce brakecylinder pressure and then subsequently to increase brake cylinderpressure, in accordance with the actual track conditions. This providesfor utilizing the maximum permissible braking eiort and thus eiectingthe shortest possible stop.

If after initiating an application of the brakes it is desired to reduceor increase the degree of the application, the pressure in the brakeapplication pipe is decreased or increased, as desired. If the pressurein the brake application pipe is decreased at a time when thecommunication between the pipe and any one of the diaphragm chambers isclosed by either of the valve units S8, 59 and l0, iluid under pressuremay be released from the chamber past one'of the check valve devices Si,82 and 83. But when the pressure in the brake application pipe isincreased, it can be increased in only those chambers which are incommunication with the brake application pipe by way of one of theaforementioned valve units. Regardless of the degree to which the brakesare initially applied, or subsequently varied, it is at all timessubject to the action of either the speed controlled switch device I3 orthe traction detector device I2.

To completely release the brakes, uid under pressure is completelyreleased from the brake application pipe 12, in which event controlValve device I I will completely release fluid under pressure from brakecylinder I9 and pipe 43. As the pressure in pipe 43 falls below the lowvalue of ten pounds, the valve device I5 disconnects the 'tractiondetector reservoir from pipe |29, and pipe |29 is connected to theatmosphere by way of port |25. As the pressure is exhausted from thispipe and the connected volumes, spring 99 returns the shoe device 95 toits uppermost position.

At the same time, the valve device I4 operates to reconnect the tractiondetector reservoir 2B to the feed valve device I3, The traction detectorreservoir is thus recharged according to the setting of the feed valvedevice. It is to be particularly observed that pressure in the tractiondetector reservoir may be adjusted by adjusting the setting of the feedvalve device, and thus the pressure which acts to press the shoe 95 tothe rail may be adjusted. The adjusting screw |95 also provides for acertain degree of adjustment of the parts.

I also wish to point out that in the event that l the control valvedevice I I is replaced by an electrical type self-lapping valve device,wherein the degree of delivered pressure is regulated according to thedegree of 'energization of the device (in which event some form ofrheostat control will be substituted for the speed controlled switchdevice I3) the traction detector device may still be applied to such asystem by substituting for the contacts associated with arm IIlIl someconventional form of rheostat. This rheostat would merely change theresistance in the circuit to the self-lapping valve winding, and thuschange the pressure delivered thereby.

I have illustrated the two valve devices I4 and I5 as being connected tothe brake cylinder and thus operating at brake cylinder pressure, but itis to be understood that these devices may be connected to any pipe orvolume which has fluid supplied thereto and released therefromconcurrently with supply to and release from the brake cylinder.

My invention is not to be taken as limited solely to a construction suchas that disclosed in the drawing, but is broadly stated and defined inthe appended claims.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent, is:

1. In a vehicle brake system, in combination, a brake cylinder, valvemeans for progressively reducing in predetermined steps the pressure offluid supplied to said brake cylinder, an element carried by the vehicleand being adapted to be depressed into and held in engagement with atrack rail as the vehicle moves therealong, and means controlled by theforce of friction between said element and said rail for controllingsaid valve means.

2. In a vehicle brake system, in combination, a brake cylinder, valvemeans for controlling the supply of fluid under pressure to and itsrelease from said brake cylinder and operable to progressively reducebrake cylinder pressure in predetermined steps, an element carried bythe vehicle, means for depressing said element into engagement with atrack rail as the vehicle passes therealong, and means governed by theforce of friction between said element and said track rail forcontinuously controlling operation 75 of saidl valve means throughoutthe brake application.

3. In a vehicle brake system, in combination, an element carried by thevehicle adapted to be depressed and held in engagement witha track? railas the vehicle passes therealong, means governed by the force offriction between said element and a track rail for controlling thedegree of application of the brakes, and `means forv cntrolling theforce with which said element is pressed against said rail accordingtothe speed of the vehicle. l

4. In a vehicle brake system, in combination,l

an yelement carried by the vehicle, means for depressing said elementlinto engagement witlliatrack rail as the Vehicle passes therealong,means governed by the force of friction vbetween said element and saidrail for co-ntrolling the degree of application of the brakes, and meansfor controlling the force with whichV said element is pressed againstsaid rail in accordance with the speed of the vehicle.

5. In a vehicle brake system, in combination,

l an element carried by the vehicle, means for depressing said elementinto engagement with ak tra-ck rail as the vehicle passes therealong,means governed by the force of friction between said element and saidrail for controlling the degree of application of the brakes, and meansfor vary- `ing the force with which saidelement is depressed againstsaid track rail in response to Variations in vehicle speed.

6. In a vehicle brake system, in combination,

a brake cylinder, means for effecting a supply 350i fluid under pressureto said brake cylinder vto eifect an application of the brakes, valvemeans operative to reduce brake cylinder pressure in predeterminedsteps, an element adapted to be held depressed in engagement with atrackr rail as i the vehicle passes therealong, and means governed bythe force of 'friction between said element and the rail for controllingsaid valve means.

'7. In a vehicle brake system, in combination, a

brake cylinder, valvemeans for controlling brake cylinder pressure andbeing `operative to reduce brake cylinder pressure in predeterminedsteps,

an element carried by the vehicle and adaptedto be depressed intoengagement with a track rail with variable forces, means governed by theforce of friction between said element and said track rail forcontrolling the operation of said pressure controlling means, and meansgoverned by the speed of the vehicle for controlling the force withwhich said element is pressed against said rail'.

8. In a vehicle brake system, in combination, a plurality of sets ofcontacts each of which corresponds to a different permissible degree ofapplicaticn of the brakes, an element adapted to be pressed intoengagement with a track rail, said element being movable according tothe force of friction between said element and said rail, and meansassociated with said element for selec tively operating said contacts.

9. In a vehicle brake system, in combination, a plurality of sets ofcontacts adapted when operated to condition the brake system for Variouspermissible degrees of application of the brakes, an element adapted tobe pressed into engagement with a track rail, said element being movableaccording to the force of friction between said element and said rail,and means governed by the movement of said element for controlling theoperation of said contacts.

`10". In a;.vel1icle brake system, in combination, a brake cylinder,valve means for controllinglini predetermined lsteps the permissibledegree of pressure establishable in sai-d brake cylinder, an elementcarried by the vehicle, means for moving 5'? said: element intoengagement with a track rail, said' element being movable in onedirection according to the force of friction between said element andthe track rail, and means for controlling the operation of said valvemeans in response 1'05 and according to movement of said. element.

l1; In a vehicle brake system, in combination, a ,brake cylinder, an armmovable through a predetermined Zone, means for varying the degree ofbrake cylinder pressure to cause it tof assume 151' a, value accordingto the position of said arm in saidv zone, and means for determining theposition of said elementy according to the tractive condition of a trackrail.

12. In a vehicle brake system, inr combination, 2o",

an element carried by the vehicle and being adapted' to be depressedinto engagement with a track rail, means providing for positioning saidelement in a horizontal direction in accordance with the force offriction between said element 25':

and said` track rail, and means for predetermining the permissibleinitial degree of application 'of the brakes in accor-dance with theinitial-horizons tal position 0f said element, and for'thereaftervaryingthe degree of the brake application as the 3G* position of said elementchanges 'dueto changes in the force of friction.

13. In a.. vehicle brake system, in combination, a brake cylinder, valvemeans for progressively varying the degree of brake cylinder pressure in354i preselected ratios, an lelement'carried by the vehicle, means fordepressing said element" into engagement with a track rail and formaintaining'said engagement as the vehicle passes along' said' rail,means providing'for movement of said 40. element in accordance with theforce of friction between said element and said rail, and meansgovernedby the movement of said element for controlling the operation ofsaid valve means.

14. In a vehicle brake system, in combination, 45,.

a brake cylinder, Valve means for controlling thedegree ofpressureestablished in said brake cyl-` inder, an element carried Vbythe vehicle, means. for moving said element into engagement with a trackrail, means for governing the force with which said element is pressedagainst said track' rail according to vehicle speed, and means governedby the force of friction between said element and said track rail forcontrolling said valve means.

15.y Ina vehicle brake system, in combination, means including anelement slidable along a track rail for progressively determining thetractive condition of the rail, and means for progressively changing thepermissible limit for the 60 degree of application of the vehicle brakesaccording to the instant determination of the tractive condition of therail,

16. In a vehicle brake system, in combination, means operated accordingto the speed of the ve-I 65 hicle, means for determining the tractivecondition of a track rail, and means controlled jointly by said twomeans for controlling the permissible degree of application of thebrakes.

17. In a vehicle brake system, in combination, 70 a device operatedaccording to the speed of the vehicle, a second device adapted to bepressed into engagement with a track rail to determine the tractivecondition of the rail, and valve means controlled by said two devicesfor limiting 75 the permissible degree of application of the brakes.

18. In a vehicle brake system, in combination, a plurality of electriccircuits which are energized or deenergized to control the degree ofapplication of the brakes, a device operated according to the speed ofthe vehicle, means including a device adapted to engage a track rail fordetermining the tractive condition of the rail, and means controlled bysaid two devices for controlling the energization and deenergization ofsaid circuits.

19. In a vehicle brake system, in combination, a plurality of electriccircuits adapted to be energized and deenergized to control the degreeof application of the brakes, speed controlled contacts connected insaid circuits, other contacts also connected in said circuits, and meansoperated according to the tractive condition of a vehicle rail overwhich the vehicle passes for controlling the operation of said othercontacts.

20. In a vehicle brake system, in combination, a brake cylinder, anelectrically operated valve mechanism for controlling the degree ofbrake :cylinder pressure to control the degree of application of thebrakes, electric circuits through which current is supplied to operatesaid electrically operated valve mechanism, a device operated accordingto the speed of the vehicle, and a second device operated according tothe tractive condition of a track rail over which the vehicle passes,said two devices and said circuits being so arranged that said circuitsare jointly controlled by said two devices.

21. In a vehicle brake system, in combination, a brake cylinder, aplurality of magnet valve devices for controlling the degree of brakecylinder pressure, a device operated according to the speed of thevehicle, traction detector means includ- .ing an element engageable witha track rail for determining the tractive condition of the rail, andmeans whereby said plurality of magnet valve devices are subjected tothe joint control of said speed controlled device and said traction,detector means.

22. In a vehicle brake system, in combination, a brake cylinder, a valvemechanism for controlling the supply of fluid under pressure to and itsrelease from said brake cylinder and being :operative to reduce brakecylinder pressure in predetermined Steps, speed controlled means, railtraction detector means, and means for subjecting said valve means tothe joint control of said speed controlled means and rail traction de-:tector means.

23. In a vehicle brake system, in combination,

an element carried by the vehicle adapted to be pressed into engagementwith a track rail, means governed by the force of friction between saidelement and said track rail for controlling the degree of application ofthe brakes, and means for varying the force with which said element ispressed vagainst said track rail.

24. In a vehicle brake system, in combination, a brake cylinder, anelement carried by the vehicle and adapted to be pressed into engagementwith a track rail over which the vehicle passes, means governed by theforce of friction between said element and said track rail forcontrolling the degree of brake cylinder pressure, and means controlledby fluid at brake cylinder pressure for controlling movement of saidelement into engagement with said track rail.

25. In a vehicle brake system, in combination, an element carried by avehicle and adapted to be pressed into engagement with a track rail overwhich they vehicle passes, fluid pressure operated means for pressingsaid element against said track rail, means for controlling the supplyof fluid under pressure to and its release from said fluid pressureoperated means, and means for varying the degree of pressure of uidsupplied to said iiuid pressure operated means as the speed of thevehicle diminishes.

26. In a vehicle brake system, in combination, an element carried by thevehicle and adapted to be pressed into engagement with a track rail overwhich the vehicle passes, a cylinder operable to press said element intoengagement with said rail with a force in accordance with the pressureof fluid supplied thereto, means for reducing in predetermined steps thefluid pressure established in said cylinder, and means controlled by avariable operating condition of the vehicle for controlling said lastmeans.

27. In a vehicle brake system, in combination, an element carried by thevehicle and adapted to be pressed into engagement with a track rail overwhich the vehicle passes, means governed by the force of frictionbetween said element and said track rail for controlling the degree ofapplication of the brakes, fluid pressure operated means for pressingsaid element against said track rail, a reservoir normally charged withfluid under pressure and being normally connected to a source of supplyof fluid under pressure, and means operative upon effecting anapplication of the brakes for isolating said reservoir from said sourceof supply and for connecting said reservoir to said fluid pressureoperated means.

J. WARREN l STAU'FFER.

